Sadiq Khan is investigating ways of introducing a pay-per-mile charging scheme to cover the future fall in Ultra-Low Emissions Zone (Ulez) revenue when more cars become compliant.
Richard Holden, the roads minister, told MPs that Seb Dance, London’s deputy mayor for transport, had told him that work was taking place in the Mayor’s office to look at how to introduce such a plan.
Mr Khan had previously hinted that London could see a Singapore-style system where sensors on gantries monitor cars’ movements, charging more for travelling at peak times.
However, preparations are already being made within Transport for London (TfL), with the body recruiting software engineers to look at the best way to implement such a scheme.
TfL has previously stressed this was just one option being looked at and would be subject to consultation.
The expansion of Ulez, set to launch at the end of August, is set to bring in £200 million in the first 12 months of being in place.
However, this figure is set to continue to drop over the coming years as more vehicles become compliant with Ulez emissions rules.
Steve Tuckwell, a Conservative councillor from the London Borough of Hillingdon, said: “Sadiq Khan’s plans to charge every single driver in Hillingdon with road user charging prove once again that he just ignores Outer London.
“If he gets his way, nobody will be safe from his war on motorists.”
The Telegraph has contacted the Mayor’s office.